At least 11 civilians, including three children, were killed on Thursday in regime barrel bomb attacks on a jihadist-held town in northern Syria, a monitoring group said.

At least 11 civilians, including three children, were killed on Thursday in regime barrel bomb attacks on a jihadist-held town in northern Syria, a monitoring group said.

Government helicopters dropped the crude and indiscriminate weapons on Al-Bab, which lies in the northern province of Aleppo and is held by the extremist Islamic State group, according to the Syrian Observatory for Human Rights.

Since Saturday, at least 68 civilians have been killed in aerial attacks on the town.

Observatory head Rami Abdel Rahman told AFP the "intensified air attacks by regime forces on Al-Bab are aimed at foiling IS efforts on multiple fronts," including the nearby Kweyris military airport, which IS has besieged for more than a year.

Al-Bab is strategically important because it is one of IS's closest positions to regime-held parts of Aleppo, he said.

In May, more than 60 civilians were killed by barrel bomb attacks on the town.

Syria's embattled regime has heavily bombarded areas in Aleppo province that have fallen out of its control.

To the west, in Idlib province, an alliance of rebels and Islamist fighters carried heavily shelled the province's last two regime-held Shiite villages for the second consecutive day.

The "Army of Conquest," an opposition coalition that includes Al-Qaeda's Syria affiliate Al-Nusra Front, began its assault on Fuaa and Kafraya on Wednesday.

"Dozens of shells fell overnight on Wednesday and into Thursday morning on Fuaa and Kafraya, which are largely inhabited by Shiite Muslims," the Observatory said.

Abdel Rahman said there were casualties but had no immediate toll.

The Army of Conquest said on Wednesday its attack was a response to an offensive by the army and the Lebanese Shiite movement Hezbollah on Zabadani, the last rebel-held bastion along the Syrian-Lebanese border.

Clashes in Zabadani raged on Thursday, according to the Observatory, which has documented heavy shelling on the town since early July.

At least 230,000 people have been killed in Syria's multi-front conflict, which began in 2011 with anti-government protests but devolved into a civil war.